Numerous systems for removing pollutants from boiler plant flue gases are known in the art. The need for such systems has become particularly acute in recent years, as environmental concerns have become more prevalent.
Among the prior art systems are those which employ heat exchanger apparatus to cool flue gases and collect the condensate, which contains pollutants from the gases. By removing the condensate, pollutants are also removed. Examples of such techniques are seen in U.S. Pat. Nos. 4,876,986 to Johnson, which employs rotating rock beds to transfer heat, and 4,597,433 to Johnson, which employs large size pebble beds to transfer heat.
Although it is thus known in the prior art that flue gas condensation contains pollutants, and that causing such condensation is one way to remove pollutants, an effective system has not been developed which both removes substantially all pollutants and is capable of being readily retrofit onto existing power plant systems.
It is therefore a general object of the invention to provide a more efficient heat exchange between boiler plant flue gas and boiler feedwater contained in the tubes around the exterior surface of which the flue gas rapidly passes.
A further objective is to make a more perfect removal of sulphur and nitrogen oxides, as well as aerosols and particulates, from the flue gas.
A third objective is to make commercially valuable byproducts from the condensate which is produced when the flue gas of fossil-fuel fired boilers is cooled and the water in the flue gas condenses.